Relatively low molecular weight, amorphous resins (usually with molecular weights ranging from 400 to 2000) are useful in many applications, including tackifying agents for adhesives, ink additives, polymer additives, rubber and tyre additives, bitumen additives, road marking resins, paper sizing and pipe wrapping. The majority of these resins are apolar but many applications benefit from polarity. There are polar resins on the market but all have drawbacks such as instability or incompatibility with apolar or low polarity polymers. Certain commercial grades of tall oil rosin esters (TOREs) or terpene phenolic resins (TPRs) are used to improve the performance of ethylene vinyl acetate (EVA)-based hot-melt adhesives (HMAs) but are incompatible with non-polar polyolefins. TOREs also suffer from color instability and odour generation at application temperatures. Hydrocarbon resins, particularly hydrogenated cycloaliphatic resins, are superior in color stability and odour generation, but do not exhibit high all-around performance on polar surfaces, such as polyethylene terephthalate (PET) and acrylic varnishes, where TOREs are often used. The adhesive industry recognizes this problem but has yet to achieve a satisfactory solution.
Thus, a need exists for a hydrocarbon resin or an adhesive component having enhanced HMA performance without the instability and odour generation normally associated with TOREs or TPRs. In the area of polymer additives, it would also be advantageous to have effective polar resins which are compatible with non-polar polyolefins. This would improve the surface polarity and enhance adhesion, printability and corona treatment retention. In co-extruded films it would also enhance the film integrity at the interface between non-polar and polar polymers, e.g. between polypropylene (PP) and polyethylene-vinyl alcohol (EVOH). It would also help the dispersion of polar fillers such as PBT, CaCO3, wood flour and nanocomposite materials. At first this desire seems contradictory but the invention described herein solves the problem.
EP 0 088 510 discloses a polar synthetic petroleum resin. A cyclopentadiene oligomer mixture is reacted with a carboxylic acid or anhydride such as phthalic or maleic acids and then hydrogenated. The reaction proceeds via the acid group reacting with the unsaturation of the resin oligomer thus forming an ester group at the point of attachment. The resulting resin product can be generally classified as a norbornyl ester.
Although the adhesive properties of compositions comprising polar synthetic resins disclosed to date are improved, their improvement is moderate. Also, the applications of these modified hydrocarbon resins and resin oligomers are limited mainly to adhesives. Another important drawback of these modified resins is the cost of manufacturing modified resins due to the large number of manufacturing steps which are necessary to produce the compositions.
The present invention aims to obviate or at least mitigate the above described problems and/or to provide improvements generally.
The grafted materials disclosed herein are believed to be produced through a different route, namely via an unsaturated bond of the acid or anhydride onto the resin which can have unsaturations but which are preferably at least partially hydrogenated and more preferably substantially hydrogenated.
Grafting functional components onto conventional hydrocarbon resins and/or resin oligomers and optionally combining the grafted resin or grafted oligomer material with another tackifying resin or other adhesive components improves performance and provides advantages over TOREs and TPRs when used in hot melt and other adhesive formulations. Particularly the performance of hydrocarbon resins, particularly hydrogenated aromatic cycloaliphatic resins, on polar surfaces can be improved by modifying the resins to include polar functionality.